The present invention relates to a process for the preparation of fluoropolyoxyalkylenes having at least one methylol end group xe2x80x94CH2OH and containing at least one chlorine atom in the other end group.
It is known in the prior art, for example GB 1,309,401 or U.S. Pat. No. 3,766,251, that the perfluoropolyethers with methylol end groups can be prepared by reduction of the corresponding perfluoropolyethers having xe2x80x94COOR end groups, wherein R is a C1-C5 alkyl group, in the presence of metal-hydrides reducing agents, such as lithium-aluminum hydride (LiAlH4), sodium-boron hydride (NaBH4), lithium-boron hydride (LiBH4), in the presence of ethyl ether, dioxane, diglyme, tetrahydrofuran, or in the case of NaBH4 in the presence of water or methanol, followed by the hydrolysis of the obtained reaction product by the aforesaid reduction.
The reduction reaction is carried out by directly adding a solution of perfluoropolyoxyalkylene alkylcarboxy ended in a solvent to a solution or suspension of the metal hydride in a solvent maintained under stirring at temperatures between 0xc2x0-100xc2x0 C.
The reaction process scheme wherein a perfluoropolyether is used with an end group xe2x80x94COOC2H5 and NaBH4 as reducing agent is as follows:
a) 2Rfxe2x80x94COOC2H5+NaBH4xe2x86x92(Rfxe2x80x94CH2O)2B(OC2H5)2Na+
b) (Rfxe2x80x94CH2O)2B(OC2H5)2xe2x88x92Na++HCl+3H2Oxe2x86x922Rfxe2x80x94CH2OH+2C2H5OH+NaCl+H3BO3 
Rf=perfluoropolyoxyalkylene chain.
The Applicant has found that it is not possible to carry out said process, with high yields and selectivity, using as starting compounds fluoropolyethers having in their structure one end group cointaining at least one Cl atom and the other end group being a carboxylic ester, to obtain the corresponding fluoropolyethers with a methylol end group.
Besides, a hardly controllable self-catalytic decomposition of the reducing agent takes place, which implies significant process risks as regards its conduction bringing to very low and non reproducible yields in the desired product.
The need was therefore felt to prepare with high yields and selectivity, by a controllable process, fluoropolyethers having one end group containing one chlorine atom and the other end group being xe2x80x94CH2OH.
The Applicant has unexpectedly found that it is possible to solve the above technical problem by starting from fluoropolyethers having one end group containing one Cl atom and the other end group a carboxylic ester to obtain with high yields and selectivity the corresponding fluoropolyethers with xe2x80x94CH2OH end groups.
It is therefore an object of the present invention a process to obtain fluoropolyoxyalkylenes having one end group containing one Cl atom and the other end group formed by a methylol group, having structure:
Txe2x80x94Oxe2x80x94(CF2CF(CF3)O)nxe2x88x921xe2x80x94(CF(CF3)O)mxe2x80x94CF2xe2x80x94CH2OHxe2x80x83xe2x80x83(I)
wherein:
T=C1-C3 perfluoroalkyl containing one Cl atom;
n=an integer from 1 to 15;
m/n=0-0.5;
m+n being such to have a number average molecular weight in the range 280-4,000, preferably 280-1,000,
said process comprising the following steps:
a) the gradual addition, in inert gas atmosphere, of a mixture formed by an aprotic or protic solvent and a reducing agent selected from the metal hydrides class, to an ester precursor having the structure
Txe2x80x94Oxe2x80x94(CF2CF(CF3)O)nxe2x88x921xe2x80x94(CF(CF3)O)mxe2x80x94CF2xe2x80x94COORxe2x80x83xe2x80x83(II)
xe2x80x83wherein T, m, n have the above meaning and R represents a C1-C20 alkyl, aromatic, cycloalkyl or heterocyclic residue, said residues being optionally substituted, maintaining the reaction mixture under stirring at a temperature in the range 0xc2x0-20xc2x0 C., preferably 5xc2x0 C.-15xc2x0 C.;
b) hydrolysis of the reaction product obtained in step a) with an aqueous acid solution, with formation of an aqueous phase and of an organic phase, and the subsequent separation from the organic phase of the compounds of structure (I) having one end group xe2x80x94CH2OH and the other one containing Cl.
The ester precursor (II) can optionally be used in admixture with an aprotic or protic solvent.
The solvents for the reducing agent and for the ester precursor can be aprotic solvents, such as for example tetrahydrofuran, diglyme, dioxane or protic solvents as for example methanol, ethanol, isopropanol, isobutanol, preferably ethanol. It is possible to use mixtures of the aforesaid solvents.
As reducing agents, metal hydrides can be used, such as for example lithium-aluminum hydride (LiAlH4), sodium-boron hydride (NaBH4), lithium-boron hydride (LiBH4) dissolved or in suspension in the above solvents. Preferably a solution or a suspension containing 0.1-15% by weight of sodium-boron hydride (NaBH4) is used. The NaBH4 amount with respect to the ester precursor (II) is comprised between the stoichiometric reaction value and an excess of 30%.
Step b) of hydrolysis and separation of the compound (I) is carried out by known methods. Generally the hydrolysis is carried out by gradually adding the reaction compound obtained in step a) to an aqueous solution of HCl, preferably at a concentration of 5-10% by weight, in an amount at least equiponderal with respect to the precursor (II). The addition of the compounds obtained from step a) to the acid solution is gradually carried out as the optional excess of the unreacted reducing agent hydrolyzes developing gaseous hydrogen. At the end of step b), several aqueous washings can optionally be carried out to completely remove the inorganic salts from the reduced fluorinated compound (I).
The hydrolysis of the reaction mixture of step a) can also be carried out by directly adding to said mixture the aqueous acid solution.
By the process of the present invention it is possible to obtain a complete conversion of the starting ester, a selectivity higher than 99% and an yield on the separated compound higher than or equal to 90%, preferably higher than or equal to 95%.
Furthermore in the present process hydrogen develops only in limited amounts with remarkable advantages as regards the conduction and safety of the process in an industrial plant.
Step a) of the process reduction of the present invention can be carried out in the presence of stabilizers of the reducing agent such the alkaline metal alcoholates, for example sodium ethylate.
The present process, characterized in that the reduction reaction is carried out by gradually adding a solution or suspension of the reducing agent to the fluoroether (II) to be reduced, can be used to reduce fluoroalkanes or fluoroethers free from end groups containing Cl but containing at least one xe2x80x94COOR end group with R as above defined.
In other words by using fluorinated esters as precursors it is possible to obtain the corresponding fluoroethers or fluoroalkanes having at least one methylol xe2x80x94CH2OH group with high conversions and selectivity higher than 99% by using a limited excess of the reducing agent, generally lower than 30% of the stoichiometric value.
As precursors to be reduced, monofunctional or bifunctional perfluoropolyethers having the following general formula:
T1xe2x80x94CFW1xe2x80x94Oxe2x80x94Rf1xe2x80x94CFW2xe2x80x94T2xe2x80x83xe2x80x83(III)
can be used, wherein:
T1, T2, equal to or different from each other, are selected from end groups of the xe2x80x94COOR type, or xe2x80x94F, xe2x80x94CF3, xe2x80x94CF2CF3 with the proviso that at least one between T1 and T2 is xe2x80x94COOR;
W1 and W2, equal to or different from each other, are F, CF3; Rf1 is a perfluoropolyoxyalkylene chain having a number average molecular weight in the range 300-10,000 comprising one or more repeating units of xe2x80x94CF2CF2Oxe2x80x94, xe2x80x94(CF2CF(CF3)O)xe2x80x94, xe2x80x94(CF(CF3)CF2O)xe2x80x94 xe2x80x94CF2(CF2)zCF2Oxe2x80x94, xe2x80x94CR4R5CF2CF2Oxe2x80x94 type;
wherein:
z is an integer equal to 1 or 2;
Y is F or CF3;
R4 and R5, equal to or different from each other, are selected from H, linear or branched perfluoroalkyl having a number of C atoms from 1 to 4;
said units being statistically distributed along the perfluoropolyoxyalkylene chain.
In particular the following Rf1 perfluoropolyethers can be mentioned as preferred:
(A) xe2x80x94(CF2CF(CF3)O)a(CFYO)bxe2x80x94
wherein Y is F or CF3; a and b are integers such that the molecular weight is comprised in the above range; a/b is comprised between 10 and 100;
or the repeating units shown in (A) can be linked as follows:
xe2x80x94(CF2CF(CF3)O)a(CFYO)bxe2x80x94CF2(Rxe2x80x2f)CF2xe2x80x94Oxe2x80x94(CF2CF(CF3)O)a(CFYO)bxe2x80x94 wherein Rxe2x80x2f is a fluoroalkylene group from 1 to 4 C. atoms;
(B) xe2x80x94(CF2CF2O)c(CF2O)d(CF2(CF2)zO)hxe2x80x94
wherein c, d and h are integers such that the molecular weight is comprised in the above range; c/d is comprised between 0.1 and 10; h/(c+d) is comprised between 0 and 0.05, z has the above value, h can also be equal to 0;
(C) xe2x80x94(CF2CF(CF3)O)e(CF2CF2O)f(CFYO)gxe2x80x94
wherein Y is F or CF3; e, f, g are integers such that the molecular weight is comprised in the above range; e/(f+g) is comprised between 0.1 and 10, f/g is comprised between 2 and 10;
(D) xe2x80x94(CF2(CF2)zO)sxe2x80x94
wherein s is an integer such as to give the above molecular weight, z has the already defined meaning;
(E) xe2x80x94(CR4R5CF2CF2O)jxe2x80x2xe2x80x94
wherein R4 and R5 are equal to or different from each other and selected between H or perfluoroalkyl, for example having 1-4 C atoms, jxe2x80x2 being an integer such that the molecular weight is the above mentioned one; said units inside the fluoropolyoxyalkylene chain can be linked each other as follows:
xe2x80x94(CR4R5CF2CF2O)pxe2x80x2xe2x80x94Rxe2x80x2fxe2x80x94Oxe2x80x94(CR4R5CF2CF2O)qxe2x80x2xe2x80x94
wherein Rxe2x80x2f is a fluoroalkylene group, for example from 1 to 4 C atoms, pxe2x80x2 and qxe2x80x2 are integers such that the molecular weight is the above mentioned one;
(F) xe2x80x94(CF(CF3)CF2O)jxe2x80x3xe2x80x94
jxe2x80x3 being an integer such as to give the above molecular weight.
(A) and (B) are the particularly preferred structures.
These structures comprising the mentioned repeating units and the methods for preparing them are described in the patents GB 1,104,482, U.S. Pat. No. 3,242,218, U.S. Pat. No. 3,665,041, U.S. Pat. No. 3,715,378, EP 148,482, U.S. Pat. No. 4,523,039, U.S. Pat. No. 5,144,092, and for their functional derivatives see for example U.S. Pat. No. 3,810,874. All these patents are incorporated herein by reference.
Compared to the processes of the prior art wherein the reduction is carried out, by adding the perfluoropolyether ester to a solution containing the reducing agent, the present process requires a lower amount of the reducing agent and it can be industrially carried out with the significant advantage that during the process lower amounts of hydrogen develop. More specifically the Applicant has found that by gradually adding the reducing agent, in solution or in suspension in a solvent, to a fluoropolyoxyalkylene carboxy-ended with the other end group containing one Cl atom, maintaining the reaction mixture at a temperature in the range 0xc2x0 C.-20xc2x0 C., it is possible to obtain the corresponding fluoropolyoxyalkylenes having methylol end groups xe2x80x94CH2OH, with quantitative conversions and yields at least equal to 90, preferably at least equal to 95%, using a limited excess of the reducing agent with respect to the stoichiometric value, and with the reduction to values lower than 1% molar in undesired by-products having one end group containing one H atom derived from the transformation of the end group containing one Cl atom.
The present invention will be better illustrated by the following Examples, which have a merely indicative but not limitative purpose of the scope of the invention itself.